In a hard disk drive (HDD), which is an example of a magnetic disk drive, a magnetic head supported by an actuator is positioned to a given track on a spinning magnetic disk to read and write data. On the magnetic disk, a data area where data are to be recorded is defined. At the end of operation of the HDD, the magnetic head is moved to a predetermined stand-by position outside the data area by the actuator and is retained at the stand-by position during non-operation of the HDD to protect data on the data area.
If a HDD receives any impact from the outside during non-operation, the actuator may rotate due to the impact so that the magnetic head may go back to the data area. On this occasion, the magnetic head may destroy data. Therefore, HDDs have latch mechanisms for latching actuators to retain the actuators outside the data area (refer to Japanese Patent Publication No. 2001-14815 “Patent Document 1”, for example). As representative latch mechanisms, magnetic latches and mechanical latches have been known in the art.
One of the typical magnetic latches has a mechanism for holding an actuator by a magnet embedded in a rubber attracting an iron chip attached to a tip end of the actuator. The magnetic latch requires a sufficient magnetic force to keep attracting the actuator so as to hold the actuator against an impact. In the meanwhile, to reduce the used amount of materials, the magnet in a voice coil motor (VCM) may be reduced in size.
The smaller the magnet, the less the torque constant in the VCM. Thus, an HDD with a smaller VCM torque constant may not be able to exert sufficient torque for pulling the actuator away from the magnetic latch at the start-up of the HDD. On the other hand, if the attracting power is reduced to be weak enough for pulling the actuator away from the magnetic latch, a problem arises that the actuator cannot be held against an impact.
Mechanical latches latch actuators mechanically so that the functions are not affected by VCM magnets like the magnetic latches. As typical mechanical latches, two-piece mechanical latches have been known in the art. A two-piece mechanical latch has a mechanism in which a long lever and a short bar are combined and can handle both of clockwise and counterclockwise external impacts. The long lever is rotated by an inertia force induced by an external force and the short bar engaged with the long lever opens and closes with the motion of the long lever to latch the actuator.
In the two-piece mechanical latch, however, when the HDD is in vibration, the long lever starts vibrating to cause harmful vibration to the HDD. Besides, for free rotation of the long lever and because of a small mounting space for the long lever, a common long lever is not fixed in the axial direction but has an amount of play, which may cause particularly large vibration. Such vibration of the mechanical latch may induce vibration of the actuator or the magnetic head to cause an error in the HDD. Since a two-piece mechanical latch requires two components of the long lever and the short bar to be used in combination, the number of components as well as the number of steps in assembling the latch will be greater so that the two-piece latch has limitations in contribution to the product cost reduction.
One-piece mechanical latches (single latches) can overcome the above-described problems in two-piece mechanical latches. A single latch has a hook for engaging with the actuator and the one-piece structure including the hook is rotated by magnetic force, the actuator, or inertia force to open or close, which in turn latches the actuator rotated by the external force. Since a single latch does not have a component corresponding to the long lever, it will not be a cause of harmful vibration to the HDD, even if the HDD is in vibration.
On the other hand, since the single latch rotates without a long lever which shows a motion similar to that of the actuator, the latch's rotational movement to open or close does not agree with the actuator's rotational movement caused by the external impact. Accordingly, it is preferable to prevent the actuator from moving to above the magnetic disk without contacting the latch by widening the swing angle range (rotation range) of the single latch.
However, if the latch engages with the actuator at one point, widening the latch's swing angle range may increase the possibility of contact between the corner of the latch's engagement surface and the actuator. If the corner of the latch's engagement surface contacts the actuator, the latch's engagement surface does not engage with the actuator's engagement surface so that the latch might more likely bounce off the actuator. This results in that the latch turns into an open state and the actuator moves to above the magnetic disk.
Accordingly, a mechanism for a single latch is demanded that can more securely latch the actuator rotated by an external force. Besides, it is preferable that a two-piece mechanical latch have a mechanism that can latch the rotating actuator more securely.